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How to check the Mozilla Firefox version?

To check your Mozilla Firefox version, open the menu (three horizontal lines) in the top-right corner, click Help, then About Firefox. The version number appears in the window that opens. You can also type about:support in the address bar and read the Version field under Application Basics.

Knowing your exact Firefox version matters for security patches, feature support, and reproducing bugs. Below are reliable methods for every platform, plus how to test your website across many Firefox versions at once.

Why Knowing Your Firefox Version Matters

Mozilla ships a new Firefox release roughly every four to five weeks, so versions move quickly. The version number tells you which security fixes you have, which web platform features are available, and whether a bug you are seeing is already resolved upstream. For developers and QA engineers, it is also the first data point when reproducing a reported defect, since behavior can differ between releases.

Check the Firefox Version on Windows and Mac

The About Firefox screen is the most reliable method because it also shows update status:

Open Firefox on your computer.
On Windows, click the menu button (three horizontal lines) in the top-right corner, then choose Help. On Mac, click Firefox in the menu bar at the top of the screen.
Click About Firefox.
A window appears showing the current version number, for example 128.0.
Firefox checks for updates in the same window and applies any pending update after you restart.

Check the Version Using the Address Bar

If you only want to read the number without triggering an update, use the internal support page. Type the following in the address bar and press Enter:

about:support

Under the Application Basics section you will see the Firefox version listed next to Version. This page also reports the build ID, update channel, and profile details, which are handy when filing a bug report.

Check the Firefox Version on Android and From the Command Line

On Android, open the Firefox app, tap the three-dot menu, tap Settings, then scroll down to About Firefox to read the version. The about:support address-bar trick works on mobile too.

On desktop, you can print the version straight from a terminal, which is ideal for scripts and CI pipelines:

# Windows, macOS, or Linux
firefox --version

# Example output
# Mozilla Firefox 128.0

Prefer a no-install check? Use the TestMu AI What version of Firefox do I have tool, or see the latest Firefox version to confirm you are up to date.

Common Mistakes and Troubleshooting

Confusing About Firefox with about:about: The correct address-bar command for version details is about:support, not about:about, which only lists internal pages.
Reading the version before restart: If About Firefox downloaded an update, the new version only applies after you restart the browser.
Confusing release channels: Firefox, Firefox ESR, Beta, Developer Edition, and Nightly report different numbers. Check the update channel on about:support.
Trusting the user agent alone: Extensions and privacy settings can spoof the user-agent string, so verify through About Firefox for the true version.
Assuming auto-update is on: Managed or enterprise installs may disable updates, leaving you on an old version without warning.

Conclusion

Checking your Mozilla Firefox version takes seconds: open About Firefox, type about:support in the address bar, or run firefox --version from a terminal. Keeping the browser current ensures you have the latest security patches and web features. And when you build or test websites, remember that your users span many Firefox versions, so validating across real browsers is the surest way to ship a consistent experience.

Frequently Asked Questions

How do I quickly check my Firefox version?

The fastest way is to type about:support in the address bar and press Enter. The version appears next to Version under Application Basics. You can also open the menu, choose Help, then About Firefox to see the version and update status.

Where is About Firefox on a Mac?

On macOS, click Firefox in the menu bar at the top of the screen, then choose About Firefox. A small window opens showing your current version number and whether an update is available.

How do I check the Firefox version on Android?

Open the Firefox app, tap the three-dot menu, tap Settings, then scroll to About Firefox to see the version. Alternatively, type about:support in the address bar and read the Version field.

Does checking the version update Firefox?

Opening the About Firefox window triggers an update check and downloads a pending update automatically, but it only applies after you restart the browser. Using about:support simply displays the version without starting an update.

How can I find the Firefox version from the command line?

Run firefox --version on Windows, macOS, or Linux from a terminal to print the installed version. This is useful for scripts, CI pipelines, and confirming the version on machines without opening the browser UI.

Why does my website look different on older Firefox versions?

Older Firefox releases may lack support for newer CSS and JavaScript features, so layouts and functionality can differ. Test your site across multiple Firefox versions on a cross-browser cloud to catch these differences before users do.